Spin turn lawn mowers are becoming popular for use in mowing lawns by both commercial lawn care operations and residential owners, displacing the conventional tractor-like mowers which are controlled via a steering wheel and a separate speed control. Spin turn lawn mowers are typically operated from the operator seat by moving one or both of a pair of pivoted control levers that are position in front of the operator seat for easy access by the operator. Forward movement of the lawn mower is accomplished by pushing forward on both pivoted control levers, while steering is accomplished by an unequal displacement of the control levers. For example, a forward moving left turn would be accomplished by pushing the right control lever forwardly more than the left control lever. The term “spin turn” is derived by the ability of these hydrostatically driven lawn mowers to be turned in place by pulling one control lever rearwardly while pushing the other control lever forwardly.
The structural configuration of many spin turn lawn mowers is that the engine is mounted on the frame of the mower over the rear wheels and behind the operator seat. The frame is supported by four wheels with the two rear wheels being driven by hydrostatic motors and pumps and the two front wheels being caster wheels that have very little weight on them. This weight distribution produces an inherent stability problem, particularly when the spin turn lawn mower is operated on wet slopes. The apparent problem with the conventional spin turn mower configuration is that the front wheels are not controlled. Thus, if either of the rear wheels loses traction, e.g. while traveling over a wet sloped lawn surface, the mower goes into a flat spin and often results in a loss of control of the lawn mower.
Manufacturers of spin turn lawn mowers have been addressing this control problem with hydrostatic control systems that are spring-biased to a neutral position so that releasing the control levers allows the control system to cease driving the mower; however, under many conditions, once the mower has started into a flat spin the mower will continue the motion until the surface conditions change. Walker Manufacturing of Fort Collins, Colo., manufactures a spin turn mower that has a single lever on the console for controlling the speed of operation of the mower and then a pair of levers centrally in front of the operator to vary the speed of each wheel individually to accomplish turns of the mower. The Walker Manufacturing control mechanism would limit the ability of an operator to make radical movements of the pivoted control levers which can cause traction loss for the mower.
In U.S. Pat. No. 5,725,068, granted on Mar. 10, 1998, to Theodore Smith, Jr., a mechanical linkage is disclosed to limit the forward speed of the hydrostatic drive to provide a more effective operation of the vehicle to rake sand traps on golf courses. An integrated steering wheel that controls the movement of the rear steering wheels is disclosed in U.S. Pat. No. 7,234,301, granted to Raymond Hauser on Jun. 26, 2007. Another version of a steering wheel control can also control the front wheels in addition to the rear steering wheels; however, such a steering mechanism is complicated in construction, although the steering mechanism does improve stability on sloped surfaces since the front wheels are placed under control by the steering mechanism.
The spring-biased neutral position for hydrostatic, spin-turn lawn mowers is disclosed in U.S. Pat. No. 7,634,953, granted to Brad Hoffman, et al on Dec. 22, 2009, and assigned to Deere & Company. An electronic system for monitoring a hydrostatic drive, and for bringing the hydrostatic drive into a safe state when a control fault occurs, is disclosed in U.S. Pat. No. 8,386,135, issued to Michael Brand, et al, on Feb. 26, 2013. A steering mechanism and ground speed control for a windrower, a hay harvesting machine that is hydrostatically driven, is taught in U.S. Pat. No. 6,523,635, Issued on Feb. 25, 2003, to Robert Johnston, et al.
Furthermore, the operation of hydraulically driven mowers is difficult to control for novice operators. The sensitivity of the lever controls results in a turn in direction of movement when one of the control levers is moved without a corresponding movement of the other control lever. Novice operators are known to have difficulty in keeping the position of the two control levers at corresponding positions, resulting is further instability of the operation of spin turn lawn mowers. Accordingly, a cruise control linkage could be desirable to enable the spin turn lawn mower to be operated in a straight line while mowing.
It would be further desirable to provide a control mechanism for a spin turn lawn mower that improves stability of the mower without changing the overall configuration of the mower. It would also be desirable to provide a control mechanism that overlies the conventional pivoted control lever system for a spin turn lawn mower to separate the forward speed control from the steering control for the mower. Providing a foot control for operating the spin turn lawn mower in either a forward or a rearward direction would be of further desirability, particularly if the control levers could be operated to override the foot controls to provide directional control.